Conventionally, it has been desired to be able to adjust the screen brightness of a display device over a wide range from “bright” to “dark” in accordance with the brightness of a room or the liking of the viewer. In liquid crystal displays among display devices, as a method of adjusting the brightness of the screen, for example, there are the two types of “backlight (B/L) adjustment” and “video signal adjustment”.
In video signal adjustment, brightness adjustment is performed by for example changing the gradation with respect to the video picture that is displayed on a screen. In the case of having performed this video signal adjustment, it is accompanied by degradation of image quality. Therefore, it is desired that this adjustment method not be used as much as possible. On the other hand, in B/L adjustment, brightness adjustment is performed by modulating the light source.
The B/L adjustment has an advantage of little degradation of the image quality of the video image that is displayed, but on the other hand, the range of being able to adjust brightness is narrow. Therefore, in this B/L adjustment, the brightness of the screen cannot be made darker or brighter than a certain value.
Therefore, an apparatus has been provided that adjusts the brightness by combining video signal adjustment and the B/L adjustment as shown in the art of Patent Document 1 given below.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. H11-0194736